JPS61112112A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To reduce the titled device at its size by constituting the device of a diaphragm for branching the reflected light of a spot on a subject into plural light beams, prisms and photodetecting elements to detect focused state. CONSTITUTION:Infrared luminous flux 11 radiated from a light emitting part 10 forms a spot on the subject 7 through a condenser lens 12 and lens groups 3, 2, 1, the reflected light is condensed by an image-forming lens 15 through a half mirror 13 and its image is formed on photodetecting parts 18, 19 through the diaphragm 16 and the prism group 17. A motor 24 is driven by a control circuit 22, the lens group 1 is moved and the image of the subject 7 is formed on a sensor 5. The luminous flux divided by the prism 17 is formed an image on the center position of the pphotodetecting parts 18, 19 to detect the focused state. Since a light source part and a range finder are stored in a zoom lens, the device can be reduced at its size and highly accurate focusing can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an automatic focus adjustment device provided in a video camera or the like.

[Background of the invention]

Conventionally, various types of automatic focus adjustment devices used in video cameras and the like have been proposed and put into practical use.

Among them, for example, as described in Tokukai No. 46-28500, there is an automatic focusing device that measures the distance to the subject by irradiating the subject with infrared rays and using the principle of triangulation. Since the configuration is simple, it has the characteristics of high reliability and low cost.

Furthermore, since this method irradiates the subject with infrared rays, it has the advantage that the focusing performance does not deteriorate even when shooting under low illumination.

However, since the principle of triangulation is used with the infrared light emitter that projects infrared light toward the subject and the infrared receiver that receives the reflected infrared light from the subject as a baseline, the distance to the subject can be measured. Accuracy depends on the length of the baseline (the length of the baseline is referred to as the baseline length). Therefore, in the conventional example of an automatic focusing device that has been implemented for a 6x FW zoom lens, the baseline length is 60 It is difficult to miniaturize the device because it is as long as ~90 degrees, and it is also necessary to provide a window for measuring the baseline length outside the zoom lens near the front lens of the zoom lens. It became.

On the other hand, with the recent demand for smaller video cameras, etc.
The screen size of image sensors is becoming smaller, for example, 2/3
The traditional 1/2 inch image pickup tube has gradually been replaced by smaller 1/2 inch and 173 inch image pickup tubes. Along with this, zoom lenses have also become smaller; for example, F
In the case of 14 6x zoom lens, conventionally 46111
1, the diameter of the front lens has been reduced to about 301,111 mm.

As described above, as each part is becoming smaller, it becomes extremely important to make the automatic focusing device smaller.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focus adjustment device that eliminates the drawbacks of the prior art described above and can be constructed in a compact size.

[Summary of the invention]

In order to achieve this object, the present invention provides an infrared emitting element and a light receiving element for distance and measurement inside a zoom lens to be focused, and uses a so-called TTL method to achieve miniaturization. It is characterized by

To this end, the above-mentioned infrared light emitting element that projects infrared rays toward the subject is provided, a light source device is provided that creates a spot on the subject when the infrared rays reach the subject, and the reflected light of the nuclear spot is collected. a diaphragm disposed behind the focusing lens, which splits the condensed reflected light into a plurality of light beams through a plurality of apertures; a prism which refracts the plurality of light beams in different directions; A distance measuring device is provided, which includes the light receiving element that receives the light flux, and a control circuit that detects a focusing state from the light receiving position of each light flux.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an automatic focusing device according to the present invention, in which 1 is a front lens group + 2h variator lens group, 511 is a compensator lens group, and 511 is a compensator. 4 is a master lens group, 5 is a senna, 6 is an optical axis of the lens groups 1 to 40, 7 is a subject, 8 is a drive circuit for the infrared light emitting element 9, 9
1'0 is the infrared light emitting element, 1'0 is a light emitting part, 11 is an infrared light beam, 12 is a condenser lens, 13 is a half mirror with a reflectance of about 50%, 914 is a mirror that reflects only infrared rays, 15
is an imaging lens, 16 is an aperture, 17 is a prism group, 18
．． 19 is a light receiving section, 20.21 is a sense circuit, 22 is a control circuit, and 23 is a front lens group position setting circuit.

24 is a seventh gear, 25 is a motor gear, and 26 is a front lens group position setting gear.

In the figure, each lens group 1 to 4 arranged on the optical axis 6
constitutes a zoom lens for forming an image of the subject 7 on the sensor 5 at a desired zoom magnification.

Among the lens groups 1 to 4, the front lens group 1 moves on the optical axis 6 by focusing, and the variator lens group 2 and the convencator lens group 3 move on the optical axis 6 by changing the magnification. An infrared light emitting element 9 that has a movable light emitting section 10 and emits long wavelength infrared light of about 800 to 900 nm emits light intermittently by a drive circuit 8 controlled by a control circuit 22.

The infrared light beam 11 emitted from the light emitting unit 10 is condensed by a condensing lens 12 having a focal length almost equivalent to the focal length of the master lens group 4, and is then condensed by a half mirror 13.
is incident on the convencator group 3 via the mirror 14,
The light passes through the variator lens group 2' and the front lens group 1 and is irradiated onto the subject 7. In this case, when focusing, the condenser lens 1
2, the focal length and setting position of the condenser lens 12 are adjusted so that the spot generated on the subject 7 by the infrared light beam has the same shape as the light emitting section 10.

The reflected light of the infrared light irradiated onto the subject 7 is reflected from the front lens group 1. It passes through the variator lens group 2° and the compensator lens group 5, is reflected by the mirror 14, and is reflected by the half mirror 13.
After passing through, the light is focused by the imaging lens 15. This focused reflected light passes through an aperture 16 and a group of prisms 17, is imaged on light receiving sections 18 and 19, and is converted into an electrical signal.

The electrical signal is then amplified by the sense circuits 20 and 21 and supplied to the control circuit 22.

The control circuit 22 controls the drive circuit 8 to cause the infrared light emitting element 9 to emit light intermittently, and also controls the sense circuit 20.2.
By processing and calculating the above electrical signals from 1,
The distance to the subject 7 is detected and a distance measurement signal representing the detection result is generated.

The front lens group position setting circuit 23 drives the motor 24 in response to the distance measurement signal, and moves the front lens group 1 in the direction of the optical axis 6 by the motor gear 25 and the front lens group position setting gear 26. .

In this way, a focused subject image can be obtained on the sensor 5.

FIG. 2 is a configuration diagram showing the distance measuring section of the automatic focus adjustment device shown in FIG. 1, in which 17L and 17 are respective prisms of the prism group 17, 18L and 18R are light receiving elements forming the light receiving section 18, and 19L. , 19R is a light receiving element forming the light receiving section 19, and 27 is a spot image on the subject 7.

29.30 is the luminous flux of the reflected light, 31.32 is the light receiving section 18.
19, and parts corresponding to those in FIG. 1 are given the same reference numerals.

Note that the infrared light reflected from the subject 7 is transmitted through the front lens group 1. The light passes through the variator lens group 21, the convencator lens group 3, and the imaging lens 15, but in the figure, for convenience, these are collectively referred to as an equivalent imaging lens 28.

In the figure, the reflected light that has passed through the equivalent convergence lens 28 and has been converged passes through 91 pairs of substantially rectangular apertures formed in the diaphragm 16, thereby forming a light beam 29 on the left side and a light beam 30 on the right side. It is branched into.

One of the left side light beams 29 is refracted downward from the incident direction by the prism 17L, and is irradiated onto the light receiving section 18 disposed on the lower side of the drawing to form a spot image 31. Also,
The right beam 30 is refracted upward from the direction of incidence by the prism 17H, and is irradiated onto the light receiving unit 19 disposed at the upper side in the drawing, showing a focused state in which an image is accurately formed.
(b) shows the state where the bond is blurred with the front focus, and (C) shows the spot image 31.32 at the center position of images 18 and 19 with the back focus.
are imaged, and these spot images 31 and 32 are imaged,
The centers of these spot images 31 and 32 are located on the light receiving element 1, respectively.
On the dividing line of 8I, 18R, light receiving element 19Lt19
Each light receiving element 181 . and 18
R.

The amounts of light received by 19L and 19R are equal. In this case, the light beams 29.50 intersect in front of the light receiving section 18.19 so that the object is also in focus on the sensor 5 (Fig. 1), so the spot image 31 is on the right side compared to when in focus. shift towards
Since the spot image 32 is also to the left and the intersection position of the light beam 29.50 is behind the light receiving section 18.19, the spot images 51.52 are shifted in the opposite direction to that shown in FIG. 0 Therefore, by knowing the positions of the spot images 51 and 52, it is possible to detect whether or not the subject image is in focus.

FIG. 5 is a block diagram showing a specific example of the control circuit 22 (FIG. 1) that performs focus adjustment, and includes 35, 54, 35
is a differential amplifier, and parts corresponding to FIGS. 2 and 4 are given the same reference numerals.

W, FIG. 6 is an explanatory diagram showing the relationship of signals of each part in FIG. 5 when out of focus.

In FIG. 5, electrical signals representing the amount of light received from the lower light receiving elements 18L and 18R are calculated by a differential amplifier 34, and an output signal A representing the difference between them is sent to one input terminal of a differential amplifier 35. Supplied.

Similarly, electrical signals representing the amount of light received from the light receiving elements 19L and 19R are calculated by a differential amplifier 56, and an output signal B representing the difference between them is supplied to the other input terminal of the differential amplifier 55. And output signal A.

An output signal C representing the difference between B and B is output from the differential amplifier 55.

Here, in the rear bin state described in FIG. 4(c), the respective output signals A, B, and C become as shown in FIG. 6(a). That is, since the amount of light received by the light receiving elements 18L and 19H is large, and the amount of light received by the light receiving elements 18R*19L is small, the output signal Ar1 of the differential amplifier 1 has a positive level, and the output signal B of the differential amplifier I1g has a negative level. The differential amplifier 35 outputs a positive level signal C.

On the other hand, in the front bin state explained in FIG. 4(b), the respective output signals A, B, and C become as shown in FIG. 6(b), and the negative values are opposite to those in FIG. A level signal is output from the difference vth amplifier 35.

When the subject image is in focus [Figure 10 (&)], the amount of light received by each of the light receiving elements 1a, , 1aR is equal to each other, and the amount of light received by each of the light receiving elements 19L + 19R Since the quantities are equal to each other, it goes without saying that the level of the output signal C of the differential amplifier 35 is zero.

In this way, the imaging state of the subject image on the sensor 5 can be detected from the signal level of the output signal C.

This output signal C is supplied to the front lens group position setting circuit 25 shown in FIG. The position of group 1 is adjusted to achieve focusing.

By the way, if the focal length of the zoom lens to be adjusted is 1
A 6x lens with a diameter of 2 to 75 tm is used, and the light emitting part 10 (Fig. 1)
The diameter of the lens is 13 m, the focal length of the condensing lens 12 is 30 m,
Assuming that the focal length of the imaging lens 15 is Sa*W, in this embodiment, the spot image 51.5 on the light receiving section 18.19 is
The diameter of 2 is approximately Q,20.

When the zoom lens is set to the telephoto side and the subject 7 moves from close to infinity, the amount of movement of the spot images 51 and 52 on the light receiving sections 18 and 19 is approximately a, 35 degrees.

In this way, when the diameters of the spots =) 31 and 52 are approximately equal to the maximum amount of movement, it is not possible to measure the distance with high accuracy unless the center of the spot image is detected accurately. In this respect, since the above embodiment uses a pair of two-split light-receiving sections 18°19, it has much higher accuracy than the conventional technology that uses one two-split light-receiving section. distance can be measured.

Next, we will discuss the reasons why the above measurements can be made with high accuracy in the seventh section.
This will be explained with figures.

Figure (a) shows a case where half of the spot image is missing due to the pattern of the subject, and Figure (b) shows the output signal level of the differential amplifier 55, 54, 35 (Figure 5) in that case. show.

As shown in the figure, even if the spot image 36°37 is partially missing, the difference in the amount of light received by the light receiving elements 18L, 18R and the difference in the amount of light received by the light receiving elements 19L, 19. Since it detects the difference in the amount of light received by can be done.

〔Effect of the invention〕

As explained above, according to the present invention, by housing the light source device and the distance measuring device inside the zoom lens, it is possible to downsize the device, and it is also possible to
It is possible to prevent the occurrence of distance measurement errors caused by infrared rays reflecting spots on the subject, which was a problem with automatic focusing devices, and enables highly accurate focusing. , it is possible to eliminate the drawbacks of the above-mentioned prior art and provide an automatic focusing device with excellent functionality.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram illustrating the relationship between the automatic focusing device according to the present invention and the focused state of an integral image, FIG. 5 is a block diagram showing a specific example of the control circuit of FIG. 1, and FIG. FIG. 7 is an explanatory diagram showing the operation of the control circuit of FIG. S, and FIG. 7 is an explanatory diagram showing the operation of the control circuit of FIG. 5 when the spot image is in the Ushiku state. 1... Front lens group 2... Variator lens group 3
...Compensator lens group 8...Infrared light emitting element drive circuit 9...Infrared light emitting element 10...Light emitting section 1
2... Condensing lens 1S... Half mirror 14...
・Mirror 15...Kuiwei lens 16...Aperture 17
... Prism group "L117B... Prism 18,
19... Light receiving section 18L, 18R, 19L, ,
19B...Light emitting element 20.21...Sense circuit 22...Control circuit 25...Front lens group position setting circuit 24...Motor 25...Motor gear 2
6...Front lens group position f#trk constant gear 55.54
．． 55...Differential amplification story 1 figure Atsushi 3 figure Prize 4 figure Sugar 5 figure

Claims (1)

[Claims] A light source device is provided inside the zoom lens, and is equipped with an infrared light emitting element that projects infrared rays toward the subject and creates a spot on the subject when the infrared rays hit the subject, and a light source device that collects the reflected light of the spot. an aperture disposed behind the focusing lens and splitting the reflected light focused by the focusing lens into a plurality of light beams through a plurality of apertures; a prism that refracts the plurality of light beams in different directions; An automatic focusing device characterized in that a distance measuring device including a light receiving element that receives refracted light beams and a control circuit that detects a focusing state from the light receiving position of each light beam is provided inside a zoom lens.